The present invention relates to a color cathode-ray tube used in televisions, computer displays, and the like, particularly to a color cathode-ray tube using a particular shadow mask.
In recent color cathode-ray tubes, in order to reduce the reflection of external light and provide a good appearance, a face panel has been made flat, and correspondingly a shadow mask also has been made flat. When the shadow mask is made flat, the flatness of the shadow mask cannot be maintained by merely supporting the body of the shadow mask with a mask frame.
Also, when merely supported with a mask frame, the shadow mask is vibrated easily by a vibration from the outside, and the display image of the color cathode-ray tube is adversely affected. Therefore, the shadow mask is stretched and fixed on the mask frame by applying a certain amount of tension to the shadow mask.
On the other hand, the impact of electron beams onto a shadow mask causes a doming in which a shadow mask surface is deformed by thermal expansion. By making the shadow mask surface flat, the displacement of an electron beam due to doming increases, particularly in the vicinities of both ends of the screen. To prevent this, the above-mentioned stretching and fixing of a shadow mask is effective because the thermal expansion due to the impact of electron beams can be absorbed by the tension.
Although irregularity in color due to doming can be prevented in the stretched type shadow mask, a vibration of the shadow mask transmitted from outside, such as a vibration transmitted from a speaker, cannot be restrained completely only by the tension applied to the shadow mask.
In order to decrease such a vibration of a shadow mask, a damper wire may be stretched on the shadow mask surface, or the damper wire may be welded to the shadow mask. However, when using such a damper wire, its shadow is reflected in the display image of the color cathode-ray tube, so that the image quality is decreased. Up to the present, various measures have been proposed for absorbing the vibration without causing such problems.
For example, JP 3-500591 A proposes a vibration attenuator including a rigid body fixed at a periphery of a shadow mask and a resistive body that is connected to the rigid body and is separated from the shadow mask. By providing such a vibration attenuator, a vibration energy is extracted from the shadow mask by the rigid body fixed to the shadow mask, and the extracted vibration energy is transmitted to the resistive body, where it is extinguished.
However, a conventional color cathode-ray tube having the above-mentioned vibration attenuator has the following problem.
In the above-mentioned vibration attenuator, the rigid body is fixed integrally to the shadow mask by welding, etc. Thus, the rigid body itself does not have the function of extinguishing the vibration energy, but strictly it is the means for extracting the vibration energy. The extracted vibration energy cannot be extinguished until it is transmitted to the resistive body, which is provided separately. Thus, such a vibration attenuator has a complex structure, which becomes a hindrance in the aspects of cost and productivity.
The present invention solves the above-mentioned conventional problem, and has an object to provide a color cathode-ray tube in which a vibration of a shadow mask can be attenuated with a simple structure.
In order to solve the above-mentioned problems, the present invention provides a color cathode-ray tube in which a shadow mask, to which a tension is applied, is held by a mask frame and is included in the color cathode-ray tube, wherein a vibration attenuator is attached to the shadow mask in a movable condition, and the vibration attenuator has a depression and is folded at the depression.
Accordingly, a vibration attenuator that can attenuate a vibration of a shadow mask can be formed easily.
That is, because the vibration attenuator is attached to the shadow mask in a movable condition, a vibration energy of the shadow mask is consumed by a friction due to the contacting and sliding of the vibration attenuator with the shadow mask, so that a vibration of the shadow mask can be attenuated with a simple structure.
Furthermore, by providing the vibration attenuator with a depression at a folding portion, folding of the vibration attenuator is made easy, and also the vibration attenuator can be attached with good precision. Therefore, a stable effect of vibration attenuation can be obtained, and also a color cathode-ray tube having a vibration attenuator not hindering the display image can be obtained.
Furthermore, in the color cathode-ray tube of the present invention, it is preferable that the vibration attenuator is formed into an approximately rectangular shape by being folded at the depression.
Accordingly, the vibration attenuator can be attached to the shadow mask easily.
Furthermore, in the color cathode-ray tube of the present invention, the vibration attenuator may be further folded at least one time at a position away from the depression to the side of an end. Accordingly, the folding distance can be controlled easily, and also a color cathode-ray tube having a vibration attenuator not hindering the display image can be obtained.
Furthermore, in the color cathode-ray tube of the present invention, it is preferable that the depression is formed by cutting or compression.
Accordingly, the depression can be formed easily.
Furthermore, in the color cathode-ray tube of the present invention, it is preferable that the depth of the depression is not more than 50% with respect to the thickness of the vibration attenuator.
Accordingly, a vibration attenuator that can be folded easily and maintains its strength can be obtained.
Furthermore, in the color cathode-ray tube of the present invention, it is preferable that the shadow mask is approximately rectangular, and the vibration attenuator is attached on a short side of the rectangle.
Because in general a shadow mask is held by a mask frame at its long sides, a large effect of vibration attenuation can be obtained by attaching the vibration attenuator on a short side of the shadow mask, which is a free end at which the amplitude of vibration becomes the greatest.